DESCRIPTION (Taken directly from the application) Cystic Fibrosis (CF) is caused by more than 500 different inherited mutations in the gene encoding the cystic fibrosis conductance regulator, CFTR. In the airway and other tissues such as the sweat gland and GI tract, CFTR is believed to regulate fluid and electrolyte movement across the cell membrane via chloride, water, and/or ATP conduction. The most common inherited CFTR mutations cause disease by disrupting normal processing pathways which in turn results in degradation of newly synthesized protein and lack of CFTR expression at the cell surface. Most remarkably, mutations which result in CFTR degradation often have only minor effects on protein function, raising the possibility that therapies which improve trafficking or block degradation might provide adequate CFTR function at the cell surface to prevent disease. A fundamental area of CF research is therefore to understand normal CFTR biosynthetic pathways, investigate how different mutations affect biogenesis, and to develop treatments to aimed at correcting these defects. Biogenesis of CFTR like most other complex integral membrane proteins involves translocation, folding, sorting and trafficking of nascent chains through the endoplasmic reticulum (ER). This process is directed in a stepwise manner by translocation machinery and protein chaperones of the ER. In the proposed work, events of wild type and mutant CFTR biogenesis will be systematically examined in cell-free and Xenopus oocyte expression systems. A major focus of these studies will be aimed at identifying mechanisms by which peptide regions are translocated across and integrate into the lipid bilayer. Truncated and chimeric vectors encoding specific regions of CFTR will be generated and used to develop assays with which to follow topological maturation and early assembly events of the nascent chain. By dissecting complex folding processes into a series of distinct steps, these studies will accomplish three important goals in understanding the molecular pathogenesis of CF. First, they define events of CFTR topological maturation and identify determinants within the chain which direct these events. Second, they identify translocation machinery through which these determinants act and assign specific assembly functions to components of that machinery. And third they will characterize the mechanism by which normal CFTR biogenesis is disrupted by inherited mutations. From this work will emerge a detailed understanding of CFTR biogenesis. Identification of specific cellular proteins involved in this process will provide new potential targets for therapy of CF and other human diseases in which protein trafficking is involved.